PURPOSE: To obtain a double shield structure for protecting a circuit to be shielded against the potential fluctuation of an inner shield case caused by noise.

CONSTITUTION: An inner shield case 4 covering a module circuit board 2 partially or entirely is grounded to a main circuit board 1 on the outside of a module case 3. Since the inner shield case is grounded to an earth pattern on the main circuit board, the earth potential of the module board does not fluctuate even if the potential of the inner shield case fluctuates thus realizing excellent noise resistance.